1. Field of the Invention
The present invention relates to a connection acceptance control scheme in a packet switching radio communication system, and, in particular, relates to a acceptance control apparatus and a new-connection acceptance control method for determining acceptance/refusal of new connection of a terminal/session based on a required communication quality of each terminal/session which requests connection.
2. Related Art
A radio communication system mainly employing an application by sound is one called a circuit switching type. This system will now be described with reference to FIG. 1.
FIG. 1 shows an outline of a channel configuration of a circuit switching type radio communication system. In the circuit switching type system, one terminal (or one session) occupies one channel, as shown in the figure. For example, when a terminal A makes a connection using a channel 1, as shown in the figure, the other terminals cannot use this channel 1.
This scheme is advantageous for the terminal A as a fixed communication quality is secured in order that no other terminals can use the channel during the communication thereof.
On the other hand, a packet switching type system is also spread for a wide use recently. This system will now be described with reference to FIG. 2. FIG. 2 shows an outline of a channel configuration according to the packet switching type radio communication system.
In the packet switching type system, information data is handled in a form of data collections called packets for transmitting it. According to this system, differently from the above-described circuit switching type system, packet including information is transmitted only when data occurs.
Although this packet switching type system has a somewhat difficulty for voice communication by the reason of severe requirement against a time delay, higher efficiency can be attained in data communication in which data to be transmitted occurs intermittently. Moreover, since each terminal transmits packets using a vacant channel, it is possible to occupy one channel by a plurality of terminals, and thus, a free time of each channel can be utilized effectively, as shown in the figure.
Although the packet switching type system is advantageous as channel use efficiency and communication efficiency can be improved, communication quality may be degraded when communication data in the entire system increases much. This problem will now be described with reference to FIGS. 3A, 3B, 4A and 4B.
FIGS. 3A and 3B show an outline of a channel configuration of the packet switching type system. First, terminals A, B, and C perform communication by using one certain channel (see FIG. 3A). Then, it is assumed that terminals D and E newly start packet communication using the same channel (see FIG. 3B). Since packets may collide and may be lost when a plurality of terminals transmit packets simultaneously by one channel, a timing of transmitting each packet should be finely controlled so as not to be transmitted simultaneously, as shown in FIG. 3B.
In case only few radio resources remain, and, thereby, a congestion state occurs, when the terminals D and E which require connection newly start using the same channel, resources allocated to the terminals (or packets) which are already under connection should be reduced so that the thus-obtained resources may be allocated to the newly participating terminals D and E. That is, the throughput on the terminals A, B, and C which have already carried out the packet transmission decreases, and the number of packets which can be transmitted thereby decreases, accordingly. Thereby, also for the terminals D and E, the number of packets used for data transmission should be limited, accordingly.
Thus, according to the related art, the resources allocated should be changed according to the number of terminals to be newly connected. Thereby, a time (or the number of packets) which can be used by each terminal for data transmission changes accordingly, and, thus, the communication quality such as a throughput may not be secured for each of all the terminals under connection.
Thus, according to the related art, not only the communication quality for the terminals on connection may not be secured, but also the communication quality for the terminals which are newly accepted for connection is not secured. Accordingly, the required communication qualities for the respective terminals may not be satisfied.
In a packet switching type system (or a circuit switching type system) in the related art, in case a connection request accompanied by a communication quality (such as a throughput, a permissible delay time, and so forth) has been made by a terminal, the system determines, based on factors such as the amount of remaining resources, magnitude of interference power, and so forth, whether or not the required quality can be satisfied, i.e., whether or not the connection can be accepted. Thus, the system controls acceptance of new connection so as to prevent the bit error rate or packet error rate from being lowered from a predetermined level.
FIGS. 4A and 4B illustrate such an acceptance control scheme performed based on interference power. FIGS. 4A and 4B typically show an outline of the acceptance control performed based on interference electric power in a packet switching type system according to the related art.
In this example, a single radio base station communicates with a plurality radio terminals, and each terminal has a buffer. It is assumed that, a terminal C newly requests a connection with a required permissible delay time in a state in which terminals A and B are on connection with the base station (see FIG. 4A).
In such a case, according to the related art, the system measures the interference electric powers on the terminals A, B, and C. Then, based on the measurement result, when it has been determined that communication quality is satisfied for all the terminals, the system gives a connection acceptance to the terminal C (see FIG. 4B).
However, when the communication quality which the terminal C requires is of a permissible delay time as mentioned above, even when the connection acceptance has been determined based on the interference electric power, the required permissible delay time may not be guaranteed for the terminal C. Thus, when the acceptance control is performed only based on a factor (interference electric power, the amount of remaining resources, etc.) other than the required communication quality factors (throughput, permissible delay time, etc.), the required communication quality of each terminal may not be satisfied.
In summary, the above-mentioned problem described with reference to FIGS. 3A and 3B occurs as a result of connection acceptance being made without previously setting the maximum number terminals which can connect by one channel, and without regarding the required communication quality of each terminal. Further, the problem described with reference to FIGS. 4A and 4B occurs as a result of connection acceptance being made not based on the parameter same as the required communication quality on each terminal.
In contrast thereto, a packet switching system may be assumed by which packet communication is performed with the maximum number of terminals which can be connected by one channel is previously set. In such a system, since the number of terminals contained in one channel does not exceed the predetermined number, the communication quality can be secured for each terminal. However, new connection is not accepted after accepting the predetermined number of terminals, even when the channel is not actually used thereby, since the number of terminals containable by one channel is previously set. Therefore, the communication channel usage efficiency may be degraded.